The invention relates to friction welding machines.
Friction welding machines are known in which two workpieces are forced together in rotational rubbing contact by pressure-applying means such as a hydraulic ram. Relatively high forces are applied to the workpieces along the axis of relative rotation and it is necessary to support the workpieces against those forces.
In known machines one workpiece is supported against those forces during welding by an abutment member which forms part of a head assembly including a rotatable chuck which rotates the workpiece. Another workpiece is supported against those forces by another fixed abutment member or backstop assembly and is steadied laterally by a clamp.
In such known machines one or the other of the abutments is acted on by the pressure-applying means. The pressure-applying means is anchored to a heavy structure which usually lies horizontally so as to form a base for the machine. The movable workpiece support is movable lengthwise of the base by the pressure-applying means and is supported upon the base. The fixed abutment member is secured to the base.
The reaction forces act on the base through the anchorage point of pressure-applying means and through the fixed abutment, and, since those two points are offset from the centre line of the base, the base is subjected to a bending moment and is deflected by those reaction forces. Where larger machines are involved, the forces are so great that the deflection in the base is relatively large. This means that accurate alignment of the workpieces on the rotational axis is impossible because the deflection of the base causes deflection of the guide surfaces on the base along which the support for movable workpiece runs.
It is also known to use tie elements or bars arranged in the same plane as the rotational axis but the use of such arrangements is very limited because for high-volume production machines the bars severely limit the freedom of movement both of workpieces as they are transferred to the machine and the successive welded components as they are transferred from the machine.
U.S. Pat. No. 3,717,295 assigned to the assignee of the present application describes and claims improved forms of construction of the base structure which reduce the adverse effect of reaction forces on the accuracy of the relative positioning of the workpieces.
In that patent it is proposed to provide the machine with transverse elements, which abut with their ends directed in one direction (e.g. upper ends) said pressure-applying means on one hand and one workpiece support on the other hand; are connected intermediate their ends by a tension tie member (which experiences tension forces); and are connected at their ends directed in the other direction (e.g. lower ends) by a pressure strut member (which experiences compressive forces).
The machine according to the present invention is a further modification and improvement over the subject-matter of U.S. Pat. No. 3,717,295.
The accuracy of positioning of the displaceable workpiece support is thus optimised under all conditions of operation of the machine.
Also, the tension member can be simplified: in particular the tension member can take the form of two or more tie bars.